John
This is nothing to do with MS Vista. There are many reasons why the
connection has failed. I presume you are using a wireless router. When
posting here you should give more details.
If it is a wireless router, then try switching it off for a minute then
switching it on again and wait (patiently) until all the little lights come
on again.
But first, have you tried simply rebooting your system? This frequently
cures minor connection problems.
With the wireless router you also have the alternative of connecting it with
an ethernet cable to your computer. If you are unaware of what an ethernet
cable is, you can Google to get a definition. With this cable you can at
least define if the system is working at all. If that doesn't work then you
may have a hardware problem somewhere.